1. Field of the Invention
This invention relates to rolling mill roll stands employing hydraulic roll position control systems.
2. Description of the Prior Art
Hydraulic roll position control systems have been employed in the past in 4-Hi strip mills (see Journal of the Iron and Steel Institute, April 1972, pp. 235-245). In this type of installation, the hydraulic roll positioning cylinders act on the bearing chocks of the backup rolls. When it becomes necessary to replace the work rolls, they and their respective bearings and bearing chocks are simply interchanged for a fresh set, while the roll housing and the backup rolls remain on the rolling line. This in turn allows the roll positioning cylinders and their hydraulic connections to the remainder of the hydraulic control system to remain undisturbed.
However, in 2-Hi mills of the type employed to roll bar products and the like, the situation is quite different. Here, the roll positioning devices must necessarily act directly on the bearing chocks of one of the work rolls. Also, work roll changes normally require an accompanying change and/or resetting of the entry and delivery guides. Thus, in order to minimize down-time, the preferred practice is to provide spare roll housings complete with fresh work rolls and pre-set guides. When a roll change is required, the on-line roll housings are removed and replaced by the spare housings.
Where the roll positioning devices comprise conventional electrically driven mechanical screwdowns, this exchange of housings does not present a problem. However, where the roll positioning devices are of the hydraulic type, an exchange of housings conventionally necessitates a breaking of hydraulic couplings in the lines connecting the roll positioning cylinders to the remainder of the hydraulic control system. When this is done, there is a danger that air may be introduced into the lines. Also, the hydraulic fluid may become contaminated by dirt, mill scale, etc. Either of these occurrences can seriously compromise the effectiveness of the hydraulic roll positioning system.